The present invention relates to a color filter manufacturing method for manufacturing a color filter by using an ink-jet head for discharging ink onto a substrate and coloring each pixel of the color filter, a color filter manufactured by the method, a display apparatus using the color filter and an apparatus including the display apparatus.
With recent advances in personal computers, especially portable personal computers, the demand for liquid crystal displays has risen, especially color liquid crystal displays. However, in order to further popularize the use of liquid crystal displays, a reduction of cost must be achieved. Especially, it is required to reduce the cost of a color filter which constitutes a large proportion of the total cost. Various methods have been tried to satisfy the required characteristics of color filters while meeting the above requirements. However, no method capable of satisfying all the requirements has been established. The respective methods will be described below.
The first method is a pigment dispersion method. In this method, a pigment-dispersed photosensitive resin layer is formed on a substrate and patterned into a single-color pattern. This process is repeated three times to obtain R, G, and B color filter layers.
The second method is a dyeing method. In the dyeing method, a water-soluble polymer material as a dyeable material is applied onto a glass substrate, and the coating is patterned into a desired shape by a photolithographic process. The obtained pattern is dipped in a dye bath to obtain a colored pattern. This process is repeated three times to form R, G, and B color filter layers.
The third method is an electrodeposition method. In this method, a transparent electrode is patterned on a substrate, and the resultant structure is dipped in an electrodeposition coating fluid containing a pigment, a resin, an electrolyte, and the like to be colored in the first color by electrodeposition. This process is repeated three times to form R, G, and B color filter layers. Finally, these layers are calcined.
The fourth method is a print method. In this method, a pigment is dispersed in a thermosetting resin, a print operation is performed three times to form R, G, and B coatings separately, and the resins are thermoset, thereby forming colored layers. In all of the above methods, a protective layer is generally formed on the colored layers.
The point common to these methods is that the same process must be repeated three times to obtain layers colored in three colors, i.e., R, G, and B. This causes an increase in cost. In addition, as the number of processes increases, the yield decreases. In the electrodeposition method, limitations are imposed on pattern shapes which can be formed. For this reason, with the existing techniques, it is difficult to apply this method to TFTs. In the print method, a pattern with a fine pitch is difficult to form because of poor resolution and poor evenness.
In order to eliminate these drawbacks, methods of manufacturing color filters by an ink-jet system are disclosed in Japanese Patent Laid-Open Nos. 59-75205, 63-235901, 63-294503 and 1-217320.
Hereinafter, a method of manufacturing a color filter according to the conventional ink-jet printing method is described.
To manufacture a color filter according to the ink-jet printing method, first, a black matrix (BM) is formed on a color filter substrate made of a glass substrate or the like. The black matrix (BM) is a light-shielding pattern used to clarify partition of each pixel for making a display screen clear. The BM is made by forming a metal thin film such as chromium or the like on a color filter substrate in correspondence with the pixel pattern by sputtering or the like. Next, a predetermined resin composition having an ink absorptive characteristic (water absorptive characteristic) is coated on the color filter substrate on which the BM is formed, whereby forming an ink receiving layer. The ink receiving layer is processed by light irradiation or heat treatment, whereby forming a hydrophilic portion (water absorptive portion where ink is absorbed) corresponding to pixels of a color filter and a water repellent portion (portion where ink is not absorbed) serving as a partition wall between pixels of the color filter. Then, ink is discharged by an ink-jet head onto the hydrophilic portion of the color filter substrate and pixels are colored.
However, according to the above-described method, positioning deviation is sometimes generated between a pattern for the water repellent portion and a pattern for the black matrix (BM). The positional offset is caused by (1) non-precise BM pattern, (2) alignment offset between the color filter substrate and a photo-mask used to form the pattern for water repellent portion. When a color filter is manufactured by the ink-jet printing method, in order to eliminate color mixture between adjacent pixels or white omission, ink must be discharged exactly in the center (portion which becomes a pixel of color filter) of two adjacent water repellent portions. Conventionally, the ink-jet head is positioned with respect to the color filter substrate by using an alignment mark as a reference, which is formed on the color filter substrate at the same time the BM pattern is formed. Therefore, the ink-jet head is precisely positioned with respect to the BM pattern, but if the pattern for the water repellent portion and BM pattern deviate as described above, positioning of the ink-jet head with respect to the pattern for the water repellent portion is offset. If the ink-jet head deviates from the pattern of the water repellent portion, defects e.g. color mixture, white omission and the like, are likely to occur.